1. Field of the Invention
The present invention relates to a waveguide coupling and in particular to a radar level indicator having a waveguide, a carrier plate and at least one feed line, wherein the waveguide is placed on a first side of the carrier plate, the feed line is routed on and/or in the carrier plate into the inner area of the waveguide and the feed line terminates with an end in the inner area of the waveguide.
2. Description of Related Art
Waveguide couplings of the type to which the invention is directed have been known for a long time in high frequency engineering and they are used as an interface between an electronic device creating an electromagnetic signal and feeding the conducted signal into the inner space of the waveguide. In waveguide couplings known from the prior art, the carrier plate normally is formed of a conventional printed circuit, wherein the feed line is often designed as a microstrip line and is led through a recess in the waveguide into the inner space of the waveguide, where the conducted electromagnetic wave is separated from the feed line and spreads as a guided electromagnetic wave in the waveguide. In use as a radar level indicator, the guided electromagnetic wave can finally leave the waveguide also as a free wave, either directly after exiting the waveguide or after passing through an emitting device attached to the waveguide, which is often provided for achieving a certain emitting characteristic; in the last case, the waveguide serves as a kind of transition element. The form of the waveguide as well as the fed electromagnetic signal determines which modes of an electromagnetic wave finally spread in the waveguide. Normally, electromagnetic waves with frequencies in a GHz range are used for radar applications.
It is known from the prior art, that the material of the carrier plate surrounding the feed line in the inner area of the waveguide is removed—for example, by means of milling—so that the end of the feed line is practically uncovered. This method is comparably complex since, in particular, for high-frequency electromagnetic waves, the resulting structures are small, and thus, mechanically damageable, so that great demands are placed on the precision of the milling to be carried out. This type of construction is known, for example, from Brumbi, D.: “Grundlagen der Radartechnik zur Füllstandmessung”, 3rd revised edition, 1999.